One of the most important maintenance tasks for HVAC systems is the periodic replacement of the air filter. This is crucial in eliminating general contaminants and improving the indoor air quality. I simple terms, there are numerous pollutants which are present in air. When these are inhaled, they will cause respiratory problems, particularly in people with allergies. Common contaminants include pet fur, pollen and dust. The filters will also improve the efficiency and performance of the appliance and prolong the HVAC lifespan.